数据结构与算法之环形队列实现（改良）

解决的初级队列无法复用的问题

public class CircleArrayQueueDemo {
    public static void main(String[] args) {
        CircleArray queue = new CircleArray(4);
        //对象接收数据
        char key = ' ';
        Scanner scanner = new Scanner(System.in);
        boolean loop = true;
        while (loop) {
            System.out.println("s(show) 显示队列");
            System.out.println("a(add) 添加数据到队列");
            System.out.println("g(get) 从队列取出数据");
            System.out.println("h(head) 查看队列头数据");
            System.out.println("e(exit) 退出");
            key = scanner.next().charAt(0);
            switch (key) {
                case 's':
                    queue.showQueue();
                    break;
                case 'a':
                    System.out.println("输入一个数字");
                    int n = scanner.nextInt();
                    queue.add(n);
                    break;
                case 'g':
                    try {
                        int res = queue.getQueue();
                        System.out.printf("取出的数字为%d\n", res);
                    } catch (Exception e) {
                        System.out.println(e.getMessage());
                    }
                    break;
                case 'h':
                    try {
                        int res = queue.headQueue();
                        System.out.printf("头数据为%d\n", res);
                    } catch (Exception e) {
                        System.out.println(e.getMessage());
                    }
                    break;
                case 'e':
                    scanner.close();
                    loop = false;
                    break;
                default:
                    break;
            }
        }
        System.out.println("程序退出");

    }
}

class CircleArray {
    private int maxSize;
    //这里的rear的定义是,指向最后一个元素的下一个位置;给最后一个元素当作标志位,实际容量是maxSize-1;
    private int rear;
    //定义是队列的第一个元素
    private int front;
    private int[] arr;

    //1.创建构造器,初始化数据
    public CircleArray(int size) {
        this.maxSize = size;
        rear = 0;
        front = 0;
        arr = new int[maxSize];
    }

    //2.判断是否为空
    public boolean isEmpty() {
        return rear == front;
    }

    //3.判断是否满了
    public boolean isFull() {
        //判断为空,并且给队列预留一个位置,动态判断
        return (rear + 1) % maxSize == front;
    }

    //4.添加方法
    public void add(int n) {
        if (isFull()) {
            System.out.println("队列满了,不能添加数据");
            return;
        }
        arr[rear] = n;
        //这里需要取模,因为到最后一个元素再添加元素的话,会出现越界,这里会使rear变为0
        rear = (rear + 1) % maxSize;
    }

    //5.取出方法
    public int getQueue() {
        if (isEmpty()) {
            throw new RuntimeException("队列空,不能取数据");
        }
        //这里把front对应的值保存一下,不然无法后移
        int value = arr[front];
        front = (front + 1) % maxSize;
        return value;
    }

    //6.显示队列方法
    public void showQueue() {
        if (isEmpty()) {
            System.out.println("队列是空的,没有数据");
            return;
        }
        for (int i = front; i < front + size(); i++) {
            System.out.printf("arr[%d]=%d\n", i % maxSize, arr[i % maxSize]);
        }
    }

    //7.定义一个返回队列有效值的方法
    public int size() {
        return (rear + maxSize - front) % maxSize;
    }

    //8.查看头数据
    public int headQueue() {
        if (isEmpty()) {
            throw new RuntimeException("队列空的，没有数据~~");
        }
        return arr[front];
    }
}